LONDON — Make no mistake, Downing Street is genuinely nervous about the referendum result. David Cameron is not hamming it up.

“They do not think they have this in the bag at all,” one source familiar with the Remain effort said. “They are already looking forward to the heartburn of watching scattered election results come in.”

Some 382 separate declarations will trickle in through the night, ranging dramatically in size and significance. Birmingham is by far the biggest count, with around 700,000 registered voters. At the other end of the spectrum, the Isles of Scilly will be one of the first to declare with just 1,700 set to cast their ballot.

The way the vote is counted will make it doubly hard to understand what’s going on until almost all the election results are in.

The U.K.’s pre-eminent polling expert, John Curtice, has warned against comparing this vote to a general election. There are no “swing seats” to look out for, no areas where small local changes can dramatically alter the national result.

In a national referendum every vote counts equally. What matters is how each area is doing against expectations.

If areas which should be comfortable for Remain start showing big shares of the vote for Brexit, then it’s really time for the prime minister to worry.

Here, POLITICO offers a guide to what to watch out for through the night.

1. Tune in at 10 p.m.

Unlike with a general election, there is no exit poll to look forward to. Instead, YouGov is carrying out a special “on the day” survey, which will be published as soon as the polls close at 10 p.m local time on Thursday.

While not as accurate as an exit poll, it may pick up a last-minute swing to one side or the other, giving the first clue in what threatens to be a long night of detective work.

2. Sunderland

It has become customary in U.K. elections for this northeastern English city to be the first to declare. In general elections it says very little about the national result, being such a Labour stronghold. But in the referendum it will provide a good early indicator of things to come.

Working-class, white and relatively poor, Sunderland is fertile Brexit territory. If Leave is seriously on the cards it needs to be comfortably ahead here. If Remain can peg back its defeat to less than 7 percent they will be happy.

Expect the result from Sunderland to be announced between 11:30 p.m and 12:30 a.m.

3. Early skirmishes

Between 1 a.m and 2 a.m, expect the flow of declarations to increase. Keep an eye out for Newcastle which needs to show a much stronger result for Remain than its great northeast rival Sunderland if the prime minister is to address the nation from Downing Street on Friday morning with a smile on his face.

At the opposite end of the country, Swindon is key. Deep in southern England and increasingly multicultural, the Wiltshire town is one of the bellwether declarations that all sides will be looking out for. If Leave’s message has cut through it’s likely to be reflected in the result here.

The town center of Swindon, a key bellweather area | Matt Cardy/Getty Images

At around 1:30 a.m, a host of ordinary English towns declare their hands, from Basildon in Essex to Stockport and Salford in Greater Manchester. If Vote Leave isn’t cutting it here, they’re going to in for a painful night.

4. Middle rounds

Top picks for anyone still up after 2 a.m: Wrexham, Lancaster and Nuneaton.

By this point, some brave pundits may start calling it one way or the other but the main broadcasters certainly won’t.

Around 22 councils are expected to declare around this time. Wrexham, a working class town in north Wales, is expected to be tight. A win for either side will be big here. By around 3 a.m, 40 percent of counts are likely to have declared. At this point, keep an eye out for Lancaster, in the northwest, which experts say is likely to mirror the national result.

Nuneaton should also offer big clues. Former Labour leader Ed Miliband’s failure to win the seat in last year’s general election was the moment most observers called the final result.

The Midlands town is Euroskeptic but full of the kind of swing voters who have backed Tony Blair and David Cameron and hold the key to a Remain win, Downing Street’s internal polling suggests.

5. Remain’s left and right hooks

Scotland and London are absolutely pivotal. If Remain doesn’t win big in both areas, Britain will be heading out of the EU. But Cameron also needs big turnouts.

Vote Leave’s own internal analysis has identified the two areas as Cameron’s biggest strengths. It was no coincidence that Ruth Davidson, the Scottish Tory leader, and Sadiq Khan, Labour’s mayor of London, were chosen to represent the Remain campaign in the final debate of the campaign Tuesday.

In Edinburgh and Glasgow as well as every borough in inner London, Remain need huge wins.

Early results in North Ayrshire and South Lanarkshire need overwhelming Remain wins. Tory Scotland also needs to come out for the prime minister — areas like Dumfries and Galloway and the Scottish Borders may help tip the balance.

6. National turnout

By around 4 a.m, pundits will be able to give a rough estimate of the turnout — Downing Street’s major concern.

Vote Leave believe anything less than 60 percent and victory is theirs. North of 70 percent favors a vote to Remain, because it suggests younger voters and middle-class professionals have turned out.

A freak turnout like in the Scottish referendum, when 85 percent voted, could see a swing back to Brexit, because it points to working-class traditional non-voters being motivated to join in — one of the most anti-EU demographics.

7. Bacon and eggs, then bed

By 5 a.m around 90 percent of the results should have been declared, including most of the strongest Leave areas. If the result is not known by this time it’s going to the wire.

For those of a nervous disposition, the official result will be announced at “breakfast time” (around 6 a.m) in Manchester. Whether the U.K. is staying a member of the EU or not will be announced by Jenny Watson, the chief counting officer for the referendum.

David Creighton

Me

Yes it is. Any delimited entity is an area. Garden, street, village, town, city, county, country continent, world, galaxy, universe and even beyond the known universe – all areas. Even Scotland.

Posted on 6/23/16 | 1:45 PM CET

Walter S

No, I disagree, Scotland isn’t an area, it’s a magical realm of unicorns and Scotch whisky.

Posted on 6/23/16 | 2:58 PM CET

Ailurus Fulens

The referendum is non-binding and the machinations involved with actually leaving the EU could take years, if they happen at all. The public is woefully uninformed on this issue. A 51/49 leave vote could result in the UK staying because the referendum is non-binding and the losing side would still be able to point to strong support.

Posted on 6/23/16 | 7:44 PM CET

AttilasDaughter

The EU destroys itself and this is just a reaction to it.
The EU does not want independent nation states.
And they don’t want the people to vote on anything.
Last years refugee crisis showed their plan.
Mix European people to destroy national identity and solidarity.
The Brexit is the starting point of the big unraveling.
Europe needs to return to nation states and have trade laws just like in the old days.
We have to return the illegal immigrants and start taking care of our own people.
The conservative national movement all over Europe has to throw out the socialist NWO creeps.

Posted on 6/23/16 | 9:32 PM CET

Thomas Peters

I have my own very unscientific indicators about the outcome.

1) The betting parlors strongly favor “Stay”, and they might be more accurate than the pollsters… again.
2) Polls show around 10% Undecided. People who wait until the last minute to choose, I believe, are more likely to vote “Stay” (the status quo) than “Leave” (the leap into the abyss). It’s human nature when in doubt to opt for what is known over the unknown, and there haven’t been any new arguments in a while.

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